Cataracts may be caused by clouding of the crystalline lens of the eye. The accepted treatment for cataracts includes cataract surgery. During cataract surgery, the affected lens is removed and may be replaced with an artificial lens.
In order to perform cataract surgery, a small incision is made in the cornea of the eye. In order to facilitate healing and avoid unnecessary damage to the eye, the incision should be made as small as possible. An instrument (or instruments) is inserted through the incision. The instrument is used to make a small opening in the anterior capsule of the lens, a membranous structure that contains the lens. This procedure is referred to as capsulorhexis. The instrument reaches the anterior capsule via the pupil. Once the opening in the anterior capsule is made, the nucleus of the affected lens may be broken into smaller pieces and removed through the opening. An artificial replacement lens may then be inserted. The replacement lens may be supported by the posterior capsule and by the structure that supports the capsule.
The opening in the anterior capsule is often made using an instrument resembling a bent needle that is inserted into the eye through the incision in the cornea. The bend in the instrument enables insertion of the point of the instrument through the pupil to the anterior capsule while avoiding the iris. The surgeon manipulates the point of the instrument, perhaps with the assistance of forceps or other instruments, so as to make a generally circular opening in the anterior capsule. An exceptionally high degree of skill may be required in order to make such an opening without tearing or jagged edges, and without causing damage to other structures associated with the lens. Tears or jagged edges may lead to uncontrolled tearing of the anterior capsule, of the posterior capsule (possibly causing exposure of the vitreous humor), or otherwise complicate the surgery and the healing process that follows.
Devices have been described previously for assisting the surgeon in performing capsulorhexis. Shechter in U.S. Pat. No. 4,911,161 describes a cutting apparatus similar to the bent needle used in traditional capsulorhexis, but provided with a mechanism for vibrating the needle. Kornefeld in U.S. Pat. No. 5,423,841 describes an intraocular knife with a controller on the handle for changing the angle of the blade during the course of cutting the anterior capsule. Such a knife may be difficult to insert through a small incision in the cornea, and may be difficult to manipulate properly during capsulorhexis. Both of these devices require the surgeon to manipulate the instrument so as to make the desired circular opening in the anterior capsule.
Other devices have been described for making a circular opening in the manner of a “cookie cutter.” Cozean, Jr. et al. in U.S. Pat. No. 5,269,787 describe a capsulorhexis apparatus with a circular cutting edge. An ultrasonic power source vibrates the cutting edge, causing it to cut a circular hole in the anterior capsule. In U.S. Pat. No. 5,873,883, Cozean, Jr. et al. describe a similarly shaped apparatus, where the circular opening is made by forcing an incompressible fluid on the anterior capsule through an annular orifice. In order to insert either of these devices into the eye, a sufficiently large incision in the cornea must be made. Such an incision may be significantly larger than an incision made during standard capsulorhexis.
Lash in U.S. Pat. No. 5,728,117 describes a capsulorhexis instrument that is designed to overcome the requirement for a large incision in the cornea. The cutting edge of the instrument may be deformed and retracted into a narrow tube for insertion through a small incision. Once inserted, the instrument is extended out of the tube where it resumes its original circular shape. The surgeon then applies pressure on the instrument, causing the cutting edge to press against and cut a circular opening in the anterior capsule. Eibschitz-Tsimhoni in U.S. Pat. No. 6,629,980 also describes an instrument that may be inserted through a small corneal incision. The described instrument has a dual-edged semicircular blade. The surgeon presses the blade onto the anterior capsule to make a semicircular cut. The blade is then turned over to make a second, reversed semicircular cut adjacent to the first, together forming a circular opening. Use of both of these instruments requires the surgeon to manually apply a regulated but relatively large amount of force to the instrument. An error made in applying such a force may result in damage to structures in the eye.
Finally, Yaacobi (U.S. Pat. No. 5,860,994) and Nguyen (U.S. Pat. No. 6,165,190) describe instruments that move a knife in a circular path in order to make a circular opening. The shapes of these instruments, with the knife extending outward from the main shaft of the instrument, may make it difficult to insert the instrument through a small incision.
Therefore, there is a need for an instrument capable of simple and safe insertion through a small incision in an outer layer, and of making a circular incision in an inner layer, while reducing the force needed to be exerted by the surgeon when using the instrument.
It is an object of the present invention to provide an apparatus and method for assisting a surgeon in making a circular incision.
Other aims and advantages of the present invention will become apparent after reading the present invention and reviewing the accompanying drawings.